I have a six-year old Rad Rover 4 with a declining battery. I'd like to replace it with a rack-mounted LiFePO4 battery (40V 20Ah) for safety and range reasons. Would I need to change any of the electronics, since the LiFePO4 discharge curve is much flatter compared to the original NMC battery? Specifically, how do I track the remaining range/state of charge?
spokewrench
Well-Known Member
- Region
- USA
I don't know, but I'm interested.
Would the new battery be a lot heavier than the old? I've read that LiFe PO4 weighs more per watt-hour than other lithium-ion batteries.
Top speed of a PM motor depends on voltage. If your hub motor was designed to top out at 20 mph on 48 volts, it might make under 17 mph on 40 volts.
Simple digital volt meters are small and cheap. Checking voltage is one way to estimate remaining charge.
Would the new battery be a lot heavier than the old? I've read that LiFe PO4 weighs more per watt-hour than other lithium-ion batteries.
Top speed of a PM motor depends on voltage. If your hub motor was designed to top out at 20 mph on 48 volts, it might make under 17 mph on 40 volts.
Simple digital volt meters are small and cheap. Checking voltage is one way to estimate remaining charge.
Thanks for the input. I mistyped; the new battery is 48V, not 40V and weighs 21 pounds, which my rear rack can easily handle. The old battery is around 8-9 pounds and is on the downtube.
spokewrench
Well-Known Member
- Region
- USA
I wonder if the LiFe PO4 could provide enough amps. (I think it probably could.) I think LiFe PO4 is supposed to last vastly longer than NMC both in charge cycles and in years.
They make them for golf carts, typically 100 AH, but Amazon has a 25 AH battery with plenty of amps and only 23 pounds. I see battery gauges for 48 V LiFe PO4 golf cart batteries, under $20.
I'm interested!
They make them for golf carts, typically 100 AH, but Amazon has a 25 AH battery with plenty of amps and only 23 pounds. I see battery gauges for 48 V LiFe PO4 golf cart batteries, under $20.
I'm interested!
harryS
Well-Known Member
The 48V ebike controller is 48V at 50% charge, and will operate between 40V a(controller cutoff) and 54.6V (full charge) for li-ion,
A 48V LFP is 51.2V nominal and charges up to 58V. Most hubmotor controllers will work that high as they don't usually have high voltage cutoffs. The RAD controller should work fine, Most can handle 52V Li-ion which charges to 58.8V max
A 20AH LFP is capble of 20A easily, Could probably push 30A without much stress. The current should be part of the battery spec anyway. How would your LCD display react? It would probably show 80% forever and then suddely drop to zero. You will have to estimate range by miles travelled,
A 48V LFP is 51.2V nominal and charges up to 58V. Most hubmotor controllers will work that high as they don't usually have high voltage cutoffs. The RAD controller should work fine, Most can handle 52V Li-ion which charges to 58.8V max
A 20AH LFP is capble of 20A easily, Could probably push 30A without much stress. The current should be part of the battery spec anyway. How would your LCD display react? It would probably show 80% forever and then suddely drop to zero. You will have to estimate range by miles travelled,
Gionnirocket
Well-Known Unidentified Member
- Region
- USA
- City
- Y. O.
Are you sure the weight, size and discharge capabilities aren't going to be an issue?
They are the very good reasons that no one is using them by default.
I'm not saying it can't be done but I wouldn't want to end up with a lame bike.
They are the very good reasons that no one is using them by default.
I'm not saying it can't be done but I wouldn't want to end up with a lame bike.
spokewrench
Well-Known Member
- Region
- USA
This one looks too good to be true. 50 amps, for 2500 watts. 25 amp hours for maybe double the range. Recharging at 40%, 15,000 cycles. 24 pounds. About $250.
(I wonder why I couldn't get the Amazon link shorter.)
Amazon won't ship large lithium batteries to my location. I don't know if this is a New York thing or restrictions by their shipper. I will search the interwebs to see if someone else has this battery and uses a shipper that will accept it. I've also seen similar batteries that have an internal SOC monitor that Bluetooth to a phone. Thanks for your advice.
Gionnirocket
Well-Known Unidentified Member
- Region
- USA
- City
- Y. O.
I guess I have different priorities when riding... but 24lbs is ridiculously heavy.
That's twice the weight of my 21Ah battery that gives me near 100mi range with a 1000w mid drive.
Where the hell are you going to mount that cinder block?
That's twice the weight of my 21Ah battery that gives me near 100mi range with a 1000w mid drive.
Where the hell are you going to mount that cinder block?
The rear rack on my fat tire bike can handle it. Part of my motivation is to avoid the fire hazard (real or imagined) of NMC lithium batteries. I'll ride around with three 1-gallon jugs of water to see how bad 24 pounds is before I buy anything.
Gionnirocket
Well-Known Unidentified Member
- Region
- USA
- City
- Y. O.
The bike can handle it but a battery up that high far from the center of gravity is going to feel like a whale tail. If you don't ride aggressively and handling is a secondary concern it may be OK for putting around.
Your test is a good idea.
PCeBiker
No-Hands No-Pedaling No-Credentials
- Region
- Canada
So could rear rack on both my ebikes.
High mounted rear weight SUCKS !!
Especially behind the rear axle.
That lifts and loosens the front end.
Don't do it unless you absolutely have to.
If there's any way to mount your battery where your current battery is, That is your Best option.
I just rode home today with a 66 pound bag of limestone dust in the box of this thing,..
It wants to wobble All Over the Fricken road.
It takes A Lot of practice to learn how to hold a straight line.
PCeBiker
No-Hands No-Pedaling No-Credentials
- Region
- Canada
Use four 1-gallon jugs filled ¾ full.
You need to get the sloshing affect happening too, if you want to learn how to handle high mount rear weight. Lol
Last edited:
Biplaneguy
Active Member
- Region
- USA
Reminds me of the day many years ago when I rode my old Schwinn Continental to the package store with a backpack for a couple of six packs of beer.
As LiFePO4 batteries are bulkier and heavier, you could split the pack and put half of them in the original location on the downtube and half on the back, that wouldn't be quite as bad.
Gionnirocket
Well-Known Unidentified Member
- Region
- USA
- City
- Y. O.
So a Bibattery guy? 
PCeBiker
No-Hands No-Pedaling No-Credentials
- Region
- Canada
Mounting a pair of smaller LiFePO4 batteries in panniers to the sides of your rear rack is a better option, if you want to mount the batteries on the rear.
Getting the weight as low as possible has a Big Affect on stability.
I tried mounting my second battery Everywhere possible on my ebikes, but I always had a wobble when I rode no-hands.
I finally managed to mount my second battery to my top tube with homemade battery brackets and now my ebike is completely stable.
I can't even get it to wobble when I try.
Similar threads
